I usually tip 20% and try to tip in cash. If I felt my service was not up-to-snuff, I'll go down to 15%. If I feel the need to tip below 15%, it is probably a situation that I would explain to the restaurant's manager. It would take a lot for me to do that - I do not want to be responsible for someone losing his or her job.

I recently had a server who made a big mistake. When I say "big," it was far from a tragedy. Instead of blame another server, blaming how busy the restaurant was, or blaming the kitchen, she simply owned up to it. She was very nervous. All of us at the table smiled at her, laughed about it, and told her how far being honest would take her. She got more than a 20% tip.

If one can't afford a substantial gratuity, he or she should refrain from dining out.